docs: def update_bounds(self, bounds):
          '''Update cylinders start and end positions
  
          '''
          starts =  bounds[:,0,:]
          ends = bounds[:,1,:]
  
          self.bounds = bounds
          self.lengths =  np.sqrt(((ends - starts)**2).sum(axis=1))
          
          vertices, normals, colors = self._process_reference()
          
          self.tr.update_vertices(vertices)
          self.tr.update_normals(normals)